A. Field of the Invention
The present invention relates to a domain-divided twisted nematic liquid crystal cell and a method for fabricating thereof.
B. Description of the Prior Art
A TN LC cell has a characteristic such that the light transmittance of each gray level varies according to the viewing angle.
FIG. 1A is a graph showing the relationship between light transmittance of the TN LC cell and voltage. FIG. 1B is a graph showing the relationship between light transmittance and the right-and-left directional viewing angle of the TN LC cell. FIG. 1C is a graph showing the relationship between light transmittance and the up-and-down directional viewing angle of the TN LC cell.
As shown in FIGS. 1B and 1C, light transmittance is symmetrical with respect to the right-and-left directional viewing angle, but light transmittance is asymmetrical with respect to the up-and-down directional viewing angle. That is, there is a region in which the gray inverts in the up-an-down directional viewing angle. Therefore, this results in a problem that the viewing angle becomes narrow. This gray inversion is caused by the alignment of the TN LC cell.
As a method of solving this problem of narrow viewing angle, a domain-divided TN LC cell (DDTN LC cell) has been proposed. The DDTN LC cell has generally been fabricated by a rubbing method or a photo-alignment method.
Fabricating the DDTN LC cell by the rubbing method, however, requires complex procedures and high manufacturing cost. For example, in the rubbing method, each substrate must undergo a polyamide or a polyimide coating process twice, photo-lithography process once, and a rubbing process once. Moreover, because the rubbing method includes a photo-lithography process, it is difficult to secure pretilt angle stability of the polyamide or polyimide alignment layer and reliability of the panel.
The photo-alignment method too has problems, such as lengthened light irradiation time. FIGS. 2A to 2D are section views showing the conventional photo-alignment process of DDTN LC cell. In FIG. 2A, a photo-alignment layer 12 is formed by coating photo-alignment material uniformly on a substrate 10. And in FIG. 2B, a first pretilt angle xcex11 is formed by light irradiation of the substrate. As shown in FIG. 2C, a first domain I is shielded by a mask 14, and additional light irradiation is performed on only a second domain II. As a result, compared with first domain I, because the quantity of light irradiation is more in second domain II, as shown in FIG. 2D, second pretilt angle xcex12 which is lower than first pretilt angle xcex11 is formed.
As previously mentioned, the conventional photo-alignment method has a problem that the overall light irradiation time becomes long. This is caused by the additional step of light irradiation and the light absorption with using the mask. Furthermore, this makes the method complex and also generates dust in the process of providing and removing the mask.
Accordingly, it is an object of the present invention to provide a simpler and more reliable method for fabricating a domain-divided twisted nematic liquid crystal cell.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention comprises: providing a first substrate having a first domain and a second domain; forming a first photo-alignment layer having a first thickness over the first domain and a second photo-alignment layer having a second thickness different from the first thickness over the second domain; and irradiating the first and second photo-alignment layers with a light to impart first and second pretilt angles different from each other, respectively.
In a further aspect, the invention comprises: a first substrate having a first domain and a second domain; and a first photo-alignment layer and a second photo-alignment layer over the first and second domains, respectively. The first photo-alignment layer has a thickness different from the thickness of the second photo-alignment layer.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.